What are you actually trying to achieve in your document? Since all good typesetting programs adjust word spacing to best fit the justification of the text, the concept of a "space" doesn't really exist. If you need to format code or something, then there are better ways to this this.
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Alan MunnJan 1 '13 at 18:17

8

Adding two consecutive spaces after an end-of-sentence period is nowadays considered old fashioned (see e.g. Bringhurst's Elements of Typographic Style). If I understand correctly, word users have to add the spaces explicitly, which is prone to errors. LaTeX can add them automatically: just put \nonfrenchspacing in your preamble (this is the default). However, if you want a modern look of your document, just put \frenchspacing in your document preamble. This is what I recommend in LaTeX and Friends.
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Marc van DongenJan 1 '13 at 19:43

@AlanMunn There are differences in spacing if \frenchspacing is disabled.
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Marc van DongenJan 1 '13 at 19:45

4

As explained by Marc van Dongen, \frenchspacing controls the amount of space added by TeX/LaTeX after a sentence independent from the number of spaces in the source code. However, putting two spaces in the source code can still be useful, as editors like Vi and Vim use them to provide navigation like "move to the end of the current sentence".
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Christian LindigJan 1 '13 at 20:04

You don't want to typeset two consecutive spaces, in general. If your aim is to have larger space after periods, it's already built in TeX:

Some words. Other words.
\frenchspacing
Some words. Other words.

will produce

Note that \frenchspacing is not the default, so we have larger space after the period in the first line.

According to TeX's rules, a normal space is inserted, with an additional space with a value set for the font, because the \sfcode for the period is 3000 (greater than 2000); in the Computer Modern font the extra space is one third of the normal interword space.

If you really want a double space after a period, you have to change the font parameter, which is not an easy task because it should be done for every font in the document.

You could also use a { }b to the same effect. I think you would be interested in reading the TeXbook or TeX by Topic – they both go over why this works. It's a subject matter called grouping.
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Sean AllredFeb 14 at 18:11